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authorJason Baron <jbaron@redhat.com>2011-08-05 16:40:40 -0400
committerIngo Molnar <mingo@elte.hu>2011-08-05 23:57:33 +0200
commitb77f0f3c1f587791aa5d9bd1b0012c9a89eb9258 (patch)
tree994a1acc79d69ae13caa965df035ae5da1828fb3 /kernel/Makefile
parent6d158f3ec537bd6d3786196b6db97fcc0f973aef (diff)
downloadlinaro-lsk-b77f0f3c1f587791aa5d9bd1b0012c9a89eb9258.tar.gz
jump label: Reduce the cycle count by changing the link order
In the course of testing jump labels for use with the CFS bandwidth controller, Paul Turner, discovered that using jump labels reduced the branch count and the instruction count, but did not reduce the cycle count or wall time. I noticed that having the jump_label.o included in the kernel but not used in any way still caused this increase in cycle count and wall time. Thus, I moved jump_label.o in the kernel/Makefile, thus changing the link order, and presumably moving it out of hot icache areas. This brought down the cycle count/time as expected. In addition to Paul's testing, I've tested the patch using a single 'static_branch()' in the getppid() path, and basically running tight loops of calls to getppid(). Here are my results for the branch disabled case: With jump labels turned on (CONFIG_JUMP_LABEL), branch disabled: Performance counter stats for 'bash -c /tmp/getppid;true' (50 runs): 3,969,510,217 instructions # 0.864 IPC ( +-0.000% ) 4,592,334,954 cycles ( +- 0.046% ) 751,634,470 branches ( +- 0.000% ) 1.722635797 seconds time elapsed ( +- 0.046% ) Jump labels turned off (CONFIG_JUMP_LABEL not set), branch disabled: Performance counter stats for 'bash -c /tmp/getppid;true' (50 runs): 4,009,611,846 instructions # 0.867 IPC ( +-0.000% ) 4,622,210,580 cycles ( +- 0.012% ) 771,662,904 branches ( +- 0.000% ) 1.734341454 seconds time elapsed ( +- 0.022% ) Signed-off-by: Jason Baron <jbaron@redhat.com> Cc: rth@redhat.com Cc: a.p.zijlstra@chello.nl Cc: rostedt@goodmis.org Link: http://lkml.kernel.org/r/20110805204040.GG2522@redhat.com Signed-off-by: Ingo Molnar <mingo@elte.hu> Tested-by: Paul Turner <pjt@google.com>
Diffstat (limited to 'kernel/Makefile')
-rw-r--r--kernel/Makefile3
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/Makefile b/kernel/Makefile
index d06467fc8f7..eca595e2fd5 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -10,7 +10,7 @@ obj-y = sched.o fork.o exec_domain.o panic.o printk.o \
kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o \
hrtimer.o rwsem.o nsproxy.o srcu.o semaphore.o \
notifier.o ksysfs.o pm_qos_params.o sched_clock.o cred.o \
- async.o range.o jump_label.o
+ async.o range.o
obj-y += groups.o
ifdef CONFIG_FUNCTION_TRACER
@@ -107,6 +107,7 @@ obj-$(CONFIG_PERF_EVENTS) += events/
obj-$(CONFIG_USER_RETURN_NOTIFIER) += user-return-notifier.o
obj-$(CONFIG_PADATA) += padata.o
obj-$(CONFIG_CRASH_DUMP) += crash_dump.o
+obj-$(CONFIG_JUMP_LABEL) += jump_label.o
ifneq ($(CONFIG_SCHED_OMIT_FRAME_POINTER),y)
# According to Alan Modra <alan@linuxcare.com.au>, the -fno-omit-frame-pointer is